The present invention relates to a method of and an apparatus for continuous metered removal of addition of small quantities of fluid over a prolonged period by producing and maintaining small uniform fluid streams.
For producing small uniform streams, a wide variety of devices were used depending on the different requirements such as capillaries or in another words very fine tubes made of glass or metal, individual bores in plates with sometimes sharp edges, cylinders provided with a notch along one surface line and arranged in a tube leaving only one passage formed by the notch and the like.
The production of such devices is technically expensive. Moreover, in such devices there is the danger that the extremely fine flow passages are blocked completely or partially by minute particles and the fluid stream is thereby completely or partially interrupted. Methods in which a fluid flows through a membrane are also known, for example reverse osmosis or dialysis. Porous membranes have been used in the past, for example for filtration, or for ultrafiltration or for separating a liquid component from a liquid, for example for separating (recovery) blood plasma from whole blood, for the oxygenation of blood, for separation of gas, for transmembrane distillation or other separation processes.
The object of all these known methods with the use of membranes is to obtain maximum fluid streams through the membranes, so called through flow rates. In the course of these methods a gradual reduction in the transmembrane fluid streams generally takes place, and the membrane consequently must be regenerated, cleaned by flushing (back) or replaced for reproducing the desired original high transmembrane fluid stream.